Lock for a bicycle



FIG. 1 is a front elevational view of a lock for a bicycle showing my new design, the rear being a mirror image of that shown;

FIG. 2 is a left side elevational view thereof, the right side being a mirror image of that shown;

FIG. 3 is a bottom plan view thereof; and,

FIG. 4 is a top plan view thereof. 

The ornamental design for lock for a bicycle, as shown and described. 